Referring to FIG. 1 of the drawings, the reference numeral 100 generally designates a conventional charge pump. Charge pump 100 generally comprises diodes D1 and D2 and capacitors CD, CS, and CP. In operation, a supplemental voltage VSUP and supplemental current ISUP are applied to the buffer capacitor and diode D1, and an alternating voltage VCLK is applied to pumping capacitor CP (which is coupled between diodes D1 and D2). Additionally, storage or buffer capacitor CS and diode D3 are coupled to output node OUT.
Turning now to FIG. 2, the operation of charge pump 100 can generally be seen. As the alternating voltage VCLK, the voltage at node VP increases, and when the voltage at node VP becomes large enough, a charge flows from capacitor CP through diode D2 to output node OUT. Then, when alternating voltage VCLK falls, the voltage at node VP falls, allowing current ISUP (through diode D1) to charge capacitor CP until capacitor CP is charged. This increase or spike in current ISUP is seen on the falling edges of the voltage VCLK in FIG. 2.
Sudden changes and other variations of the supply current ISUP, though, generate noise, which is generally undesirable. So, in order to reduce the amount of noise, a capacitor CD is used at the input of the charge pump, which serves to provide charge during the peaks of supply current ISUP. However, even with a buffer capacitors CD, noise can not be sufficiently reduced. Therefore, there is a need for a charge pump with reduced noise.